The present invention relates to well servicing fluids and additives which include a water soluble polycondensate containing phosphorous and nitrogen and to a process for making the same; and more particularly to such fluids and additives which contain or comprise a water-soluble polycondensate of a phosphomethylated amine aldehyde.
In well drilling, a drilling fluid servicing fluid or mud is pumped down through the drill stem of the rotary rig, circulated around the drill bit and returned to the surface through the annular passage between the drill stem and the well wall. The drilling fluid lubricates the drill stem and bit, cools the bit and carries the cuttings from the bit up to the surface. The drilling fluid also provides a hydrostatic head against the walls of the well to contain downhole geo-pressure.
Typical drilling fluids contain a number of additives, each satisfying a specific purpose. For example, additives are used to control the rheology of the fluid, to improve its filtration properties and/or increase its density. Notwithstanding the cost associated with such additives, the overall cost of the drilling operation is decreased by the improvement made by these additives on the drilling rate and hole-cleaning processes.
In drilling for oil or gas, there are generally three zones that require different drilling fluid characteristics. The first zone extends from 0 to 5000 feet, while the second and third zones range from 5000 to 7000 feet and greater than 7000 feet, respectively. During the initial stage of drilling, i.e., the first zone of the well, a relatively large bore hole is usually desired. In other words, a relatively large quantity of drill cuttings must be moved to the surface. This requires a well servicing fluid with excellent capacity as indicated by a high yield point which ranges from 20 to 30 pounds per 100 square feet and a plastic viscosity of 3 to 6 centipoise.
As the drilling operation gets deeper, smaller bore holes are drilled, resulting in smaller amounts of cuttings. However, the drilling fluid travels longer distances under higher pressure and is subjected to higher temperature.
The additives for the first zone are usually referred to as viscosifiers while the additives for the second and third zones are typically referred to as thinners or dispersants. The second and third zone drilling fluids must have relatively high yield point to viscosity ratio in the range of about 0.6:1.20 and must be very stable to shear and thermal stresses, because of the longer distances under higher pressure and higher temperatures in these two zones.
During these drilling operations, the drilling fluid is monitored and adjusted to obtain the desired characteristics at various depths and under varying conditions. For example, there are three fluid properties which are monitored. These properties are viscosity, yield point and fluid loss. And in general, it is desirable to maintain these properties constant over the longest possible duration. It is also desirable to use additives which are compatible with other materials in the drilling fluid, to use thermally stable non-toxic additives, to avoid excessive usage and to prevent environmental pollution.
Dispersants (thinning agents) are materials that are usually added to reduce resistance to flow and to impede the development of a gel structure. These materials have a relatively large anionic component which is adsorbed on a positive edge site of clay particle thus reducing attractive forces between the particles and resulting in a dispersion action. Generally, improved dispersion leads to reduced filtration. Examples of dispersants include polyphosphates, tannins, lignins, lignosulfonates, etc.
A wide variety of drilling fluids have been used. For example, clay based drilling fluids have been used for cooling and particle removal. In fact, the U.S. patent to Hori, U.S. Pat. No. 4,519,923, discloses the use of sodium carboxymethyl cellulose as a water loss reducing agent to be included in drilling mud. Hori also discloses the use of sulfoethylcellulose alkali metal salts as a water loss reducing agent.
In addition, the U.S. patent of Alexander, U.S. Pat. No. 3,872,018, discloses a "fluid loss" control at temperatures over 300.degree. F. (149.degree. C.) in clay-free seawater mud by the addition of polyvinyl alcohol with starch and that urea with the polyvinyl alcohol further increases temperature stability. As stated in that patent 2 to about 10 pounds per barrel of polyvinyl alcohol is sufficient. And, the average molecular weight of the polyvinyl alcohol ranges from at least about 170,000 to over 200,000.
Another approach for a high temperature stable fluid low control system is disclosed by Green, U.S. Pat. No. 4,473,480. Green discloses a combination of (a) silicate or alumina silicate material; (b) a chemical compound capable of converting to a higher oxidation state under alkaline conditions; and (c) a reaction product formed between a polymeric material selected from polyvinyl alcohol or hydroxyalkyl cellulose and a cross linking agent. Green discloses reacting a polyvinyl alcohol having an average molecular weight of between 90,000 to 200,000 with an aldehyde such as formaldehyde or melamine formaldehyde.
Lignosulfonate is a commonly used additive of this group of chemicals. Several patents disclose the modification of lignosulfonates (LS) to improve their thermal stability or thinning ability (Detroit, U.S. Pat. No. 4,447,339, and Chen et al., U.S. Pat. No. 4,521,578). According to an article [Lauzon, R. V. Oil Gas J. 80,93 (1982)] this improvement can be realized if the hydroxyl group of a lignosulfonate is oxidized to a carboxylic group. The presence of the weak acid (carboxylic) group and strong acid (sulfate) group leads to more repulsion and increased dispersion of the clay particles which adsorb the lignosulfonate chains.
Another approach to improve the thermal stability of lignosulfonate is disclosed by Blackmore, U.S. Pat. No. 4,322,301, where he grafted lignosulfonate and acrylic acid or derivatives thereof to which a phosphate or a particular metal or both were added. The use of heavy metal salts of lignosulfonates wherein the metals are chromium, aluminum, iron, copper, or combinations thereof, has been disclosed in U.S. Pat. No. 2,935,473 to improve the thermal stability of drilling fluids. While the thermal stability of these additives, especially the chromium salt and the grafted copolymer of lignosulfonate with acrylic acid in the presence of metal or phosphate, has been sufficient in some cases, they are unstable in deeper wells where the temperatures are very high. The filtration loss of fluids also increases at these depths.
Another class of thinning agents have been reported in U.S. Pat. No. 3,956,140 where sulfonated phenol-formaldehyde resins were used. Reacting urea with the sulfonated phenol-formaldehyde was effective in heat stabilizing the drilling fluid while reacting melamine with the same resin improved the filtration properties of the fluid.
The use of sulfonated amino aldehyde resins as drilling mud additives is disclosed by Lahalih et al., U.S. Pat. No. 4,839,095. As reported therein, thermal stability is achieved by the use of sulfonated urea formaldehyde while filtration properties are improved by the use of sulfonated melamine formaldehyde. However, neither sulfonated urea formaldehyde nor sulfonated melamine formaldehyde improve both thermal stability and filtration properties simultaneously. For example, when sulfonated urea formaldehyde is used, filtration losses of the drilling fluid are high while thermal stability is acceptable and when sulfonated melamine formaldehyde is used filtration losses are reduced significantly, but the yield point and thermal stability suffer.
Therefore, it is the object of the present invention to provide improved well servicing fluids and additives for controlling the rheology of the fluid, improving its filtration properties and increasing its density without adversely affecting the overall costs of the drilling operations. It is a further object of the invention to provide well servicing fluids and additives with improved thermal stability and which are stable when subjected to high shear stresses under high pressure. It is also an object of the invention to provide a process for making such fluids and additives.